Dr. Sekyung Chang Profile

Dr. Sekyung Chang

at Materials and Electrochemical Research Corp

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Publications (2)

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Proceedings Article | 21 May 2011 Paper

High-performance spinel ceramics for IR windows and domes

Juan Sepulveda, Raouf Loutfy, Sekyung Chang, Sharly Ibrahim

Proceedings Volume 8016, 801604 (2011) https://doi.org/10.1117/12.883474

KEYWORDS: Spinel, Polishing, Ceramics, Domes, Transparency, Transmittance, Contamination, Air contamination, Optics manufacturing, Refraction

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High performance spinel ceramic is required for near-term future applications based on the excellent spinel transmission properties in the UV-VIS-Mid IR wavelength range. Windows as large as 30"x60" and hemispherical domes 4"-7" in diameter have been distinguished as applications where the novel spinel technology could be successfully applied. Future applications involve the use of even more complex 3-D shapes like spinel superdomes and tubes. The thickness of some of these components has reached 1" and above. MER has been actively pursuing these design objectives and has shown the feasibility of producing some of these complex shaped parts. Optimization of transmittance and strength are always the main objective. MER has also been pursuing edge bonding technology, where large thick panes will be edge bonded into a final large window. The production of monolithic windows as large as 18"x22", which can be used as individual windows or as panes prior to edge bonding, has also been demonstrated. Using the complex 3-D spinel process, MER has also demonstrated the feasibility of producing 4"-7" diameter hemispherical domes blanks of very high quality. After rendering and polishing, defect free domes have been produced. The process has been characterized and qualified using an optical grade spinel specification. Details of MER's technology to produce low cost, high strength, transparent magnesium aluminum spinel windows and domes are described. High optical and IR transparency in the 0.3 - 5.5 μm wavelength range is obtained. Equibiaxial strength averages 180-200 MPa, with individual readings reaching 300-320 MPa maximum. Spinel optical and mechanical properties are provided.

Proceedings Article | 28 April 2009 Paper

Advances in spinel ceramic technology for large windows and domes

Juan Sepulveda, Raouf Loutfy, Sekyung Chang, Sharly Ibrahim, Nick Traggis

Proceedings Volume 7302, 73020E (2009) https://doi.org/10.1117/12.819222

KEYWORDS: Spinel, Domes, Transparency, Ceramics, Polishing, Surface finishing, Magnesium, Photonics, Aluminum, Infrared technology

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This paper describes MER's recent advances on the development of high strength, transparent magnesium aluminum spinel technology for large IR windows and domes. The novel spinel material exhibits high optical and IR transparency in the 0.2 - 5.5 μm wavelength, is very resistant to abrasion, with density higher than 99.9% of theoretical, with very fine and uniform grain size, and flexural strength of 300 MPa. Spinel domes technology has been scaled up to produce hemispherical 180° aperture domes in sizes up to 7" in diameter using freeze casting technology to produce the green dome preforms. MER is also pursuing the production of large size spinel windows by either producing monolithic large single windows or by edge bonding several smaller size windows. Both approaches present challenges. Production of monolithic large size windows is limited by equipment size, availability, and investment capital while the edge bonding approach requires perfect transparency and strength at the bonded edge. MER together with Precision Photonics Corp. are developing high strength, edge bonded, transparent magnesium aluminum spinel windows for next generation aircraft and other defense armor applications which require windows as large as 30"x30"x0.5" at an affordable cost. MER has further improved strength of the spinel by accurate control of the average grain size and grain size scatter while remarkable transmission is obtained by elimination of the intergrain/intragrain porosity, and by eliminating all possible contamination. The spinel bonding technology under development consists of chemically activated direct bonding (CADB®), an epoxy-free solution-assisted optical-contacting process developed by Precision Photonics Corporation (PPC).

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